1. Field of the Invention
This invention relates to editing information stored in a data file and, more particularly, to automatically optimizing the positioning of a record head while using an information storage medium such as a magnetic tape recorder in editing a magnetic tape or a disc recorder in editing a disc store.
2. Description of Related Art
In editing information such as video signals or audio signals or almost any other signal stored in some storage media such as on a magnetic tape, a function known as "edit optimization" has typically been performed during the editing session.
It is known that edit optimization includes manually adjusting an edit recording machine so as to provide longitudinal tracking and rotating scanner phase, which match that of the tape, which is to be edited. Tracking, for example, of a helical record head, typically allows for the subsequent longitudinal adjustment or alignment of the tape to match the helical position of the record head. Edit optimization is typically performed prior to the actual editing function and is typically useful to set up, or to initialize, or to synchronize, or to align the various elements of an edit recording machine including the storage medium so that an "optimized" edit does occur. For example, edit optimization is usually required when making "interchange edits," which are edits of a storage medium such as tape, which has been recorded by one recorder, which is different than a second recorder being used for the edit session. That is, in an interchange edit, the storage medium was written using a first machine but is being edited using a second machine.
In a typical edit optimize, longitudinal tracking is varied across the storage medium such as a magnetic tape in order to obtain a peak radio frequency (rf) amplitude signal from a record head during a playback. Note that, in an edit optimize, it is typical that a record head serves two functions, i.e. in one function, the record head is used to write information on the storage medium while, in the second function, the record head is used to read information from the storage medium. A direct current (dc) voltage representing the rf amplitude level is generally supplied to a control system, which, in turn, varies the tracking across the tape by way of a suitably programmed microprocessor within the control system until a value corresponding to the maximum rf level is detected and stored in the microprocessor. More particularly, it is known that the microprocessor monitors the rf amplitude while varying a reference signal supplied to the conventional control track circuit of the tape recorder. When the microprocessor detects the peak rf amplitude, the microprocessor stores the reference signal as a digital value corresponding to the control track position. This stored value is thereafter used to provide proper tracking.
In recent state-of-the-art digital video tape recorders such as the VPR.RTM. 300, which is a D2 composite digital format video tape recorder manufactured by Ampex Corporation, the edit optimization procedure may be facilitated by various features provided in, for example, an "edit optimize menu" which includes the necessary machine control and display indications to a human operator which allow automatic adjustments of the required parameters to perform the edit optimization.
A subtle problem with known edit optimization procedures relates to the fact that record heads need to be positioned over the tracks that are already recorded on the magnetic tape. Therefore, as newly written tracks are written over old tracks that are already recorded on the magnetic tape, an edge of the previously recorded track will typically be trimmed during the edit process when overwriting the previously recorded track. In that manner, the track is made with an improper width. However, if an edit optimization process uses the center of the track as a reference, it can align the newly recorded material with the previously recorded material.
Further, proper tracking during the editing process may not be possible due to variations in the data content of the signals already recorded on the storage medium, whether the data content be video or analog or otherwise or whether the data content be digital or analog or otherwise. The variations in the data content cause frequency variations commensurate with the different data patterns which make up the recorded data which, in turn, affects the rf amplitude of the signals on the storage medium. Such an effect is generally known by the term "pattern sensitivity." In particular, variations in frequency cause variations in the rf amplitudes due to the nature of a digital recording, particularly when using a code that changes its frequency spectrum as, for example, does a Miller-squared code. Thus a data pattern, which is recorded on a storage medium at different frequencies, will likely be played back at different rf amplitudes. It is worth pointing out that the effect of pattern sensitivity exists in analog recording as well as in digital recording, although to a much lesser extent in analog recording.
As earlier mentioned, data content variations such as typically related to changes in the scenery in the television art, cause problems in the peaking of the tracking due to fluctuations in the rf amplitude reproduced from a recording of the scenery on a magnetic tape in a video tape recorder. That is, these fluctuations are often caused not only by mistracking with the playback head but also by the variations in the data content of the recording. It follows then that, when performing, for example, an edit optimize, the pattern sensitivity can cause misleading information to be generated and the misleading information can affect the peak rf amplitude measurement. Since proper tracking is assumed upon detecting a peak rf amplitude, if the pattern sensitivity causes misleading information to be generated, then an improper alignment of a track may be signaled during an edit optimize. If an insert edit is thereafter undertaken with such an improper alignment from the edit optimize, then the insert edit could result in a poor quality and a visually unacceptable edit when the result is later viewed on a television monitor. Thus, pattern sensitivity in a digital recording, such as a recording using, for example, Miller-squared encoding or any code that changes its frequency content, will be played back with some rf amplitude variations because of the change in frequency. For example, assume a data pattern is recorded on tape at a frequency of 30 megahertz (MHz) and assume the same data pattern is recorded on tape at a frequency of 10 MHz. Upon playback, the 30 MHz frequency signal will likely have a lower rf amplitude than will the 10 MHz frequency signal due to the usual losses that occur with increased frequency.